Velocity sensitive passenger vehicle trailer brake controller

ABSTRACT

A method of controlling a trailer brake system using a trailer brake controller positioned within a passenger vehicle is provided. The method includes obtaining intended braking inputs and developing an effective baseline trailer brake controller output profile based thereon. The method scales the effective baseline trailer brake controller output profile in response to an adjustable gain setting set by an operator. A vehicle velocity is obtained and used to calculate a correction factor to the effective baseline trailer brake controller output profile. The effective baseline trailer brake controller output profile is then adjusted using the correction factor to generate a corrected trailer brake controller output signal.

CROSS REFERENCE

This application is a Continuation of co-pending U.S. application Ser.No. 11/160,644, filed Jul. 1, 2005 herein incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a passenger vehicle brakecontroller and more particularly to a passenger vehicle trailer brakecontroller.

BACKGROUND OF THE INVENTION

Passenger vehicle transport capacity is an important design aspect ofmodern vehicles. The ability to haul objects and equipment is often asimportant as the vehicle's ability to transport additional passengers.Solutions aimed at increasing a vehicle's hauling capabilities must notonly be directed at improving the vehicle's utility but must also bedirected towards improving a vehicle's safety and performance whileaccomplishing this task. One traditional approach towards improving avehicle's transport capabilities has been through the addition of atrailer attached to the vehicle. Trailers allow for a wide range ofitems to be transported by a vehicle, often without impacting transportcapabilities of the vehicle's passenger compartment.

Passenger vehicles commonly control trailer braking through the use of atrailer brake controller located within the vehicle. The trailer iscommonly equipped with electrically actuated trailer brakes. An operatorsets the gain on the controller, where the gain dictates how muchelectrical output is generated by the controller for a given set ofvehicle inputs. The controller utilizes a brake input signal incombination with the user set gain to generate a brake control signal.It is known that this signal can take different forms, such as a dutycycle output or DC voltage output. This control signal is sent to theelectrically actuated brakes which are thereby utilized to effectuatebraking within the trailer. Systems such as described translate vehicleinput, such as brake pedal force or position, brake pressure or vehicleacceleration, into a brake control signal which is adjustable accordingto the operator set gain. The brake control output signal, in turn,energizes the trailer brakes, which subsequently generates a brakingtorque on the trailer wheels.

Although the aforementioned systems may benefit from a lack ofcomplexity, they fail to address the real world principles of mechanicsthat electrically actuated dual-servo drum brake assemblies are subjectto. At increased velocities, it is known that the effectiveness ofdual-servo brake torque is reduced and therefore a given brake controlsignal generates less effective brake torque at higher vehicle speedsthan it did at lower vehicle speeds. As such, trailer brake performancedegenerates at higher vehicle speeds. It would be highly desirable tohave a trailer brake control apparatus and method that compensated forthe loss of effective brake torque at increased vehicle speeds such thata consistent brake torque could be generated over the entire range ofexpected vehicle speeds.

It is further known, that a brake torque desirable over a broad range ofvehicle speeds may be undesirable at low vehicle speeds. At low vehiclespeeds, electric dual-servo drum braking systems are subject tosignificant increases in effectiveness wherein an applied brake torquemay result in the brakes locking up (also known as “grabbiness”) ratherthan incrementally applying braking friction. Existing electric trailerbraking systems commonly fail to address this known phenomenon andthereby produce undesirable vehicle low-speed results. It would,therefore, be highly desirable to have a trailer braking system thatimproved low-speed performance by reducing brake-grab.

Finally, if one is to consider vehicle speed in the development of abrake control signal, it is important to consider the issues involvedwith accurate velocity calculation. Measurement of vehicle velocitybased on wheel speed is subject to a host of errant readings due toautomotive performance conditions. During rapid deceleration, it isknown that a wheel may generate excessive slip relative to the roadsurface. In such circumstances, if vehicle speed was estimated basedsolely on this wheel in deep slip, the estimate would be lower than theactual vehicle speed. Similarly in rapid acceleration if a wheel breaksaway from the road surface it may result in a velocity value abnormallyhigh. In other circumstances, such as vehicle turns, outer wheels mayexperience a velocity increase while inner wheels a decrease. Thus itwould be further beneficial to develop an improved method of calculatingvehicle speed prior to its utilization in effecting the trailer brakecontrol signal.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide apassenger vehicle braking system with an integrated trailer brakecontroller. It is a further object of the present invention to provide apassenger vehicle braking system with velocity sensitive performance.

In accordance with the objects of the present invention, a method ofcontrolling a trailer brake system using a trailer brake controllerpositioned within a passenger vehicle is provided. The method includesobtaining intended braking inputs and developing an effective baselinetrailer brake controller output profile based thereon. The method scalesthe effective baseline trailer brake controller output profile inresponse to an adjustable gain setting set by an operator. A vehiclevelocity is obtained and used to calculate a correction factor to theeffective baseline trailer brake controller output profile. Theeffective baseline trailer brake controller output profile is thenadjusted using the correction factor to generate a corrected trailerbrake controller output signal.

Other objects and features of the present invention will become apparentwhen viewed in light of the detailed description of the preferredembodiment when taken in conjunction with the attached drawings andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a trailer brake controllerin accordance with the present invention;

FIG. 2 is an illustration of an automotive dash assembly illustrating anembodiment of communication elements intended for use with the presentinvention;

FIG. 3 is a detail of the communication elements illustrated in FIG. 2,the communication elements are intended for use with a trailer brakecontroller in accordance with the present invention;

FIG. 4 is a block diagram of an embodiment of the trailer brakecontroller in accordance with the present invention;

FIG. 5 is a flow diagram of an acceleration sensitive vehicle velocityalgorithm for use in the present invention;

FIG. 6 is a graph of gain adjusted effective baseline trailer brakecontroller output profiles for use with the present invention; and

FIG. 7 is a detail of an effective brake torque curve as illustrated inFIG. 6, the detail showing an embodiment wherein brake torque isincreased with increased vehicle velocity.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIGS. 1 to 4, which are illustrations of a trailerbrake controller 10 in accordance with the present invention. Thetrailer brake controller 10 is intended for integration into a passengervehicle braking system. It is further intended that the trailer brakecontroller 10 be designed, assembled, and sold with the passengervehicle such that its control characteristics can be properly set by thevehicle manufacturer for a specific passenger vehicle. Additionally, byintegrating the trailer brake controller 10 into the passenger vehiclethrough manufacture, assembly and distribution, control and displayfeatures for the trailer brake controller 10 may be professionallyintegrated into the passenger vehicle 12 design. Thus, appearance,performance, safety, and customer convenience may be improved.

The trailer brake controller 10 utilizes control element 11 having anintended braking input 14 (such as a brake pressure input) and a vehiclespeed input 16 in order to adjust the trailer brake output 18. It iscontemplated that the intended braking 14 and vehicle velocity 16 inputsmay be utilized to adjust trailer brake output 18 in a variety offashions. One advantage of the present invention is that therelationship of the trailer brake output 18 to the brake pressure input14 may be adjusted for the particular vehicle 12 in which the trailerbrake controller 10 is mounted.

It is contemplated that the intended braking input 14 and the vehiclespeed input 16 may be supplied by a variety of sources within thevehicle 12. In one embodiment, however, it is contemplated that theintended braking input 14 and the vehicle speed input 16 are suppliedthrough a communication between the vehicle brake control system 22(such as the antilock braking system or electronic stability controlsystem) and control element 11. It is known that modern tow vehiclebrake control systems 22 (such as ABS) contain sensors that can be usedto estimate vehicle speed. By placing the vehicle brake control system22 in communication with the control element 11, the vehicle speed input16 may be easily estimated. Finally, the vehicle brake control system 22may be utilized to communicate to the control element 11 when the system22 has been activated. This can allow the trailer brake controller 10)to tailor its output 18 such that the trailer brakes works moreefficiently with the vehicle brake control system 22. It should beunderstood that although the vehicle brake control system 22 may beutilized to supply both the intended braking input 14 and the vehiclespeed input 16, in alternate embodiments, the intended braking input 14may be supplied through a variety of known devices or sensors such asvehicle brake pressure 24, brake pedal force 66, brake pedal travel, orvehicle accelerometer. Again, although specific embodiments have beendescribed that provide a brake pressure input 14 and a vehicle speedinput 16, a variety of methods of obtaining these inputs would beobvious to one skilled in the art in light of this application.

It is intended that the trailer brake output 18 be capable ofcontrolling a plurality of embodiments of trailer brakes. Although avariety of trailer brake outputs 18 are contemplated by the presentinvention, one embodiment contemplates the trailer brake output 18taking the form of an electrical output. In addition, the trailer brakecontroller 10 may include a variety of additional components to increaseits functionality and performance. A brake indicator lamp output 26 maybe used in conjunction with the trailer brake output 18 to improve thesafety and performance of the trailer brake controller 10. Similarly, adiagnostic input/output 28 may be included such that the trailer brakecontroller 10 may provide self diagnostic information concerning thetrailer 30 and controller 10 to a service technician. This trailer brakeelectrical output 18 not only provides power to the trailer brakes, butby monitoring the electrical characteristics of this signal, the trailerbrake controller 10 can inform a vehicle operator of improper electricalconnection with the trailer or of damage to the trailer brake'selectrical system 70. Power supplies 34, ignition run/start inputs 36,and other known elements may be utilized in conjunction with the presentdesign to provide basic functionality, concepts well known in the art.

It is further contemplated that the trailer brake controller 10 mayprovide communication between the control element 11 and theowner/operator. Although this communication can take on a variety offorms, in one embodiment it is contemplated to take the form of adisplay 42, a user control input 44 (such as a gain input control) andan override switch 46. These communication elements 48 can be adaptedand complimented to provide a range of communication and control to theowner/operator. Similarly, although these communication elements 48 maybe positioned in numerous locations, one embodiment mounts them to thevehicle dash 50 (see FIGS. 2 and 3). By equipping the vehicle with sucha control system during design and manufacture, the appearance of thecommunication elements 48 can be significantly improved and therebyincrease customer satisfaction. The display 42 can include a gaindisplay 52 and a signal strength display 54. The signal strength display54 allows the owner operator to visualize the trailer brake output 18signal and adjust the gain input control 44 to suit individualpreferences. The override switch 46 can be operated by theowner/operator to apply the trailer brakes independently of the vehiclewithout braking. It is further contemplated that the display 42 may beutilized to communicate to the owner any improper connections ordiagnostic faults determined by the control element 11. This can serveto increase the safety and awareness of the owner by properly apprisingthem of the status of their trailer's operation.

A novel feature of the present invention is derived from the methodologyit invokes to develop a velocity tailored trailer brake output signal18. A key innovation which enables velocity-sensitive trailer brakecontrol is development of a generic trailer brake torque vs. speed vs.voltage mapping 19 preferably developed using laboratory testing oftrailer brakes on a chassis dynamometer. By sweeping trailer wheelrotational speed and electric brake input voltage, while measuring braketorque output, the data shown in FIG. 6 can be collected for a singletrailer brake or across the range of available electric trailer brakingsystems, considering critical noise factors, such as piece-to-piecebrake system variability, brake lining wear, brake magnet wear and braketemperature. While the magnitude of the individual torque curves varyacross trailer brake types, the characteristic decrease in torque asspeed increases at higher voltages is adequately similar to create ageneric relationship which can be used in open loop trailer brakecontrol, as described earlier in this patent. The fact that the operatoris required to set TBC gain for given trailer conditions providesadequate adjustment of the torque/speed/voltage mapping for a giventrailer brake system.

The mapping curves 19 illustrated in FIG. 6 are contemplated to bemultivariate curves dependent on intended braking inputs 14 and vehiclespeed input 16 and therefore are in actuality three-dimensional plots.The curves 19, however, are represented as two-dimensional plots forsimplification and clarity of discussion. The curves are representativeof an effective baseline trailer brake controller output profile 60utilized by the present invention. The customer set gain 62 can then beutilized to scale this effective baseline trailer brake controlleroutput profile 60. It should be understood that a variety of scalingtechniques and generic mapping techniques may be utilized in order toimprove performance. Furthermore, although a single modified and scaledeffective baseline trailer brake controller output profile 60 has beendescribed, it should be understood that a plurality of differing orindividually tailored profiles 64) may be utilized. The intended brakinginput 14 is intended to include any existing measurement of vehiclebraking such as brake pedal force 66, brake fluid pressure 24, orsimilar methodology (see FIG. 4). It should be further understood thatthe determination of the effective baseline trailer brake controlleroutput profile 60 need not constitute a specific calculation step butmay remain defined simply by the intended braking inputs 14 and vehiclespeed input 16.

The effective baseline trailer brake controller output profile 60 isindicative of the brake torque applied by the trailer brakes if thetrailer brake output was produced under existing operational conditionsand a constant supply voltage. As supply voltage is changed this profilechanges, but the same downward trend shape exists over a range of supplyvoltages. A flaw of electric dual-servo drum brakes 70, as shown in FIG.6, is that as vehicle speed 16 increases, a given trailer brakecontroller output 18 will produce reduced brake torque. Each of theeffective baseline trailer brake controller output profiles 60corresponds to a trailer brake controller output voltage scaledaccording to a plurality of available operator gain settings 62 (gainsettings are effectively what determine the supply voltage). As can beseen, however, from the effective baseline trailer brake controlleroutput profiles 60, as vehicle speed 16 increases, the effective braketorque begins to drop. This generates different braking performance aswell as different braking feel as speeds increase.

The present invention, however, includes logic within the trailer brakecontroller 10 adapted to adjust the trailer brake output 18 such thatthis drop off in effective brake torque is neutralized. The presentinvention obtains the vehicle velocity 16 (or trailer velocity) and usesthis in conjunction with the effective baseline trailer brake controlleroutput profile 60 to determine an unadjusted output 71 and an estimateof effective brake torque loss 73. The unadjusted output 71 is simply avalue representative of a particular location along the effectivebaseline trailer brake controller output profile 60. The logic is thenadapted to calculate a correction factor 74 that compensates for theeffective brake torque loss 73 such that a constant brake torque 76 isachieved throughout the velocity range of the trailer. Although thesecalculations or steps are presently described in terms indicative ofindividual steps by the logic, it is equally contemplated that linearregression may be performed on the mapping values 19 such that thecorrection factor 74 may be directly computed from the intended brakinginput 14 and velocity input 16. The unadjusted output 71 is adjusted bythe correction factor 74 to generate a corrected trailer brake outputsignal 75 that compensates for lost torque. The correction factor 74 canautomatically make any range of partial corrections within the range ofavailable supply voltage to provide a constant brake torque 76. In analternate embodiment, the correction factor 74 may be utilized toincrease the effective brake torque 72 as velocity increases (see FIG.7). This allows a gradual ramp up in torque as speed increases.

The preceding discussion involved compensating for effective braketorque losses at increased vehicle velocities. It is known, however,that trailer brake performance suffers at low vehicle velocities aswell. The low velocity performance issues arise from the physics ofelectrically actuated dual-servo drum brakes. At very low vehiclespeeds, namely less than ten miles per hour, application of theunadjusted output 71 can result in brake grabbing or temporary seizing.This provides undesirable feel to the operator. The present invention,therefore, further includes logic adapted to utilize the correctionfactor 74 to reduce brake grabbing. This is accomplished by decreasingthe trailer brake output 18 at low vehicle speeds 16 to the point wherebrake grabbing is alleviated. Although a simple reduction in controlleroutput may be implemented, the present invention contemplates thedevelopment and use of a brake torque reduction curve 78 specificallyadapted to minimize brake grab while maintaining optimal brakingperformance.

The present invention thereby contemplates the use of a correctionfactor 74 to improve the effective baseline trailer brake controlleroutput profile 60 at both low and high vehicle speeds 16. As thecorrection factor 74 is dependent on vehicle speed 16 input, the presentinvention contemplates an improvement in estimation of vehicle speed 16through the use of vehicle dynamic status 80 (such as accelerationstatus) available from other vehicle systems (see FIG. 5). The presentinvention includes logic adapted to calculate the wheel speed 82 at aplurality of wheel locations 84. The wheel locations 84 are contemplatedto encompass individual wheel locations such as Right Front 86, LeftFront 88, Right Rear 90 and Left Rear 92. The wheel locations 84 arealso intended to encompass readings such as the use of a differentialspeed sensor 94 which may be substituted for the rear wheel readings 90,92. It is further contemplated that the wheel locations 84 may includetrailer wheel locations 96 as opposed to the aforementioned towedvehicle locations. The present invention then determines if anacceleration event 98 is present. An acceleration event 98 is intendedto encompass positive acceleration 100 (commonly just referred to asacceleration) in addition to negative acceleration 102 (commonlyreferred to as deceleration). The present invention uses theacceleration 98 to selectively choose one of the wheel speeds 82. Thevehicle velocity 16 is then set based on the selectively chosen wheelspeed 82.

It is contemplated that both the selective choosing of a wheel speed 82in addition to the use in setting vehicle velocity 16 may be achieved ina variety of fashions. In one embodiment, when a positive acceleration100 event is recognized, the wheel speeds are simultaneously compared.The slowest 104 of these wheel speeds 82 is then chosen and the vehiclevelocity 16 is set as this slowest wheel speed 104. Similarly, duringnegative acceleration 102, the wheel speeds are compared and the fastestwheel speed 106 is selectively chosen and set as the vehicle velocity16. Each of these chosen wheel speeds is then compared to physicallimits of acceleration and if the change in this speed compared to thepreviously stored speed is outside of these limits, the newly storedspeed is only advanced/decreased within the physical limit range.

Although a single wheel speed 104,106 may be utilized using this logic,it is contemplated that multiple wheel speeds 82 may be alternatelyutilized. In this embodiment vehicle acceleration 98 is utilized toselectively remove at least one of the wheel speeds 108. The logic isthen adapted to calculate the vehicle velocity 16 and thereby thecorrection factor 74 based on the remaining wheel speeds 110. In oneexample, during deceleration 102, if a wheel speed indicates zero it isreasonable to assume that wheel is locked-up and therefore is removedfrom velocity calculations. In another example, during acceleration 100,an unreasonably high value indicates wheel slippage and therefore isremoved. These two methodologies are not exclusive. During deceleration102, if the fastest wheel speed 106 is selectively chosen, any wheelspeeds 82 inconsistent with the fastest wheel speed 106 can be removedfrom the velocity calculation. The remaining velocities may be averagedor used in other algorithms to calculate a vehicle velocity 16.Similarly during acceleration 100, the slowest wheel speed 104 may beselected and any inconsistent values removed.

The present invention contemplates that the logic adapted to translateindividual wheel speed 82 into vehicle velocity 16 may be accomplisheddirectly within the trailer brake controller 10 by way of measuringwheel speed 82 using a plurality of wheel speed sensors 112, each ofwhich located at one of the vehicle wheel locations 84. The individualwheel speeds 82 may be communicated to the trailer brake controller 10wherein the selective choosing or selective removing may beaccomplished. In an alternate embodiment, however, it is contemplatedthat the vehicle velocity 16 maybe calculated using the aforementionedmethodologies using logic within the anti-lock braking system 23. Insuch an embodiment, it is contemplated that an output portal 114 beintegrated into the anti-lock braking system 23 such that the trailerbrake controller 10 may be placed in communication therewith duringassembly through the use of a communication cable or similar data link.In this way, the anti-lock braking system 23 is adapted to portinformation to a host of vehicle systems.

While particular embodiments of the invention have been shown anddescribed, numerous variations and alternative embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

What is claimed is:
 1. A method of controlling a trailer brake systemusing a trailer brake controller positioned within a passenger vehiclecomprising: receiving intended braking inputs and a vehicle speed;accessing a predetermined torque vs. speed vs. voltage data chart forthe trailer brake system; estimating an effective brake torque loss fromthe torque vs. speed vs. voltage data chart based on the intendedbraking inputs and the vehicle speed; determining a correction factor tocompensate for the estimated effective brake torque loss, the correctionfactor is determined from the predetermined torque vs. speed vs. voltagedata chart; applying the correction factor to generate a correctedtrailer brake controller output signal that compensates for lost torque,2. The method as claimed in claim 1, wherein the step of determining thecorrection factor from the data chart further comprises the step ofapplying multivariate regression analysis for the intended brakinginputs and the vehicle speed.
 3. The method as claimed in claim 1,wherein the step of applying the correction factor to generate thetrailer brake controller output signal further comprises applying thecorrection factor within a range of supply voltages to reduce braketorque as vehicle speed increases.
 4. The method as claimed in claim 1,wherein the step of applying the correction factor to generate thetrailer brake controller output signal further comprises applying thecorrection factor within a range of available supply voltages togradually increase trailer brake torque as vehicle speed increases. 5.The method as claimed in claim 1, wherein the step of applying thecorrection factor to generate the trailer brake controller output signalfurther comprises applying the correction factor within a range ofavailable supply voltages to maintain a constant brake torque.
 6. Themethod as claimed in claim 1, wherein the step of receiving intendedbraking inputs and vehicle speed further comprises receiving intendedbraking inputs and vehicle speed from an anti-lock braking system. 7.The method as claimed in claim 6 wherein the step of receiving vehiclespeed from an anti-lock braking system further comprises the steps of:measuring wheel speed at each of a plurality of vehicle wheels;determining if a deceleration event is present; and setting the vehiclevelocity to a measured wheel speed that is a greatest of the measuredwheel speeds when a deceleration event is present.
 8. The method asclaimed in claim 6 wherein the step of receiving vehicle speed from ananti-lock braking system further comprises the steps of: measuring wheelspeed at each of a plurality of vehicle wheels; determining if anacceleration event is present; and setting the vehicle velocity to ameasured wheel speed that is the smallest of the measured wheel speedswhen an acceleration event is present.
 9. The method as claimed in claim1, wherein the step of receiving intended braking inputs and vehiclespeed further comprises receiving intended braking, inputs and vehiclespeed from an electronic stability control system.
 10. The method asclaimed in claim 9 wherein the step of receiving vehicle speed from theelectronic stability control system further comprises the steps of:measuring wheel speed at each of a plurality of vehicle wheels;determining if a deceleration event is present; and setting the vehiclevelocity to a measured wheel speed that is a greatest of the measuredwheel speeds when a deceleration event is present.
 11. The method asclaimed in claim 9 wherein the step of receiving vehicle speed from theelectronic stability control system further comprises the steps of:measuring wheel speed at each of a plurality of vehicle wheels;determining if an acceleration event is present; and setting the vehiclevelocity to a measured wheel speed that is a smallest of the measuredwheel speeds when an acceleration event is present.
 12. A trailer brakecontroller for use in a passenger vehicle towing a trailer, the trailerbrake controller comprising: a controller including logic adapted toreceive intended braking inputs and vehicle speed from one of ananti-lock braking system or an electronic stability control system; thecontroller including logic adapted to access a predetermined trailerbrake controller output profile and scale the predetermined trailerbrake controller output profile in response to an adjustable gainsetting set by an operator; the controller including logic adapted toaccess a plurality of stored baseline trailer brake controller outputprofiles; the controller including logic adapted to select one of theplurality of stored baseline trailer brake controller output profilesdependent upon the intended brake inputs and the vehicle speed to set acorrection factor; and the controller including logic adapted to adjusta trailer brake control output signal using the correction factor. 13.The trailer brake controller as claimed in claim 12 further comprisinglogic adapted to set the correction factor to increase brake torque forincreased vehicle speeds.
 14. The trailer brake controller as claimed inclaim 12 further comprising logic adapted to set the correction factorto decrease brake torque for decreased vehicle speeds.
 15. The trailerbrake controller as claimed in claim 12 further comprising logic adaptedto set the correction factor to maintain a constant: brake torque atincreased vehicle speeds.
 16. The trailer brake controller as claimed inclaim 12 wherein the controller further comprises logic adapted to:receive a measured wheel speed for each of a plurality of vehiclewheels; determine the presence of a deceleration event; and set thevehicle speed to a greatest of the measured wheel speeds when thedeceleration event is present.
 17. The trailer brake controller asclaimed in claim 12 wherein the controller further comprises logicadapted to: receive a measured wheel speed for each of a plurality ofvehicle wheels, determine the presence of an acceleration event; set thevehicle speed to a smallest of the measured wheel speeds when theacceleration. event is present.